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Author Topic: Where is the "edge" of the Universe?  (Read 6302 times)

paul.fr

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Where is the "edge" of the Universe?
« on: 18/05/2007 19:46:28 »
erm...Where is the "edge" of the Universe?


 

Offline kdlynn

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Where is the "edge" of the Universe?
« Reply #1 on: 18/05/2007 20:02:13 »
OH MY GOSH!!!! i have always wondered this. everyone says it's never ending but that just doesn't seem possible!! this question usually keeps me busy for days... i can't figure it out! hopefully someone else can!
 

another_someone

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Where is the "edge" of the Universe?
« Reply #2 on: 18/05/2007 20:28:24 »
What do you mean by 'the edge of the universe'?

The universe is about 13 billion years old, thus by definition, we cannot see anything that is more than 13 billion light years away (because light simply would never had time to reach us from further away, and since nothing can travel faster than light, so nothing else from further away could possibly have yet reached us).

So, for all practical purposes, the universe has an edge that is about 13 billion light years away (but constantly getting further away as the universe gets older).  What is beyond that, we simply cannot know, because nothing from further away can reach us to tell us what is there.
 

paul.fr

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Where is the "edge" of the Universe?
« Reply #3 on: 18/05/2007 20:30:32 »
So, there is an edge. But that edge is not static! it just keeps expanding?
 

Offline kdlynn

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Where is the "edge" of the Universe?
« Reply #4 on: 18/05/2007 20:34:43 »
is something else getting smaller as the universe expands?
 

another_someone

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Where is the "edge" of the Universe?
« Reply #5 on: 18/05/2007 21:05:16 »
So, there is an edge. But that edge is not static! it just keeps expanding?

There is, for practical purposes an edge, insofar as a point beyond which we cannot see; but ofcourse, it is not an edge in the sense that with most things we think of an edge between one known thing and another known thing, but as edge between the knowable and the unknowable.

And, yes, it does keep expanding.

Ofcourse, if the universe ever goes from being a Big Bang, to a Big Crunch, and thus if at some time in the future the matter within the universe stops expanding, and starts to compact; this boundary between the knowable and the unknowable will still continue to expand, and so matter would start to be comming back through that boundary.

I am tempted to say that this fact alone would seem to make it unlikely that there ever will be a Big Crunch.

It must also be said that the edge of the universe is not absolute but relative - i.e. the edge of our Universe is about 13 billion light years away from us; but for someone living on a planet 3 billion light years away from us, he too will see an edge to his Universe that is 13 billion light years away from him, but his sphere of 13 billion light years will be centred on him, while our 13 billion year sphere will have a centre that is 3 billion light years away from his sphere, because it will be centred on us.
« Last Edit: 18/05/2007 21:10:10 by another_someone »
 

another_someone

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Where is the "edge" of the Universe?
« Reply #6 on: 18/05/2007 21:06:07 »
is something else getting smaller as the universe expands?

Not that we are aware of (or at least nothing that I am aware of).
 

paul.fr

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Where is the "edge" of the Universe?
« Reply #7 on: 18/05/2007 21:44:09 »

There is, for practical purposes an edge, insofar as a point beyond which we cannot see; but ofcourse, it is not an edge in the sense that with most things we think of an edge between one known thing and another known thing, but as edge between the knowable and the unknowable.

And, yes, it does keep expanding.


Assume we are at the centre of the universe, and have our compass points. Is the universe expanding more in a north - south directon, east - west or at all points?
 

another_someone

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Where is the "edge" of the Universe?
« Reply #8 on: 18/05/2007 21:52:44 »
If we are talking about expansion of the universe with regard to the expansion of the event horizon of the universe (rather than the Hubble expansion), then inherently we must always be at the centre of our own event horizon, and that event horizon must always be expanding equally in all directions.  Fir the event horizon to expand faster in one direction than another would require that the speed of light be different in one direction than another.
 

paul.fr

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Where is the "edge" of the Universe?
« Reply #9 on: 20/05/2007 21:18:07 »
Ok. if the universe is expanding in all directions, what "space" is it occupying! Is it taking over an area, part of space that was not within our universe? or, as it expands is it creating new "space", or something else?
 

another_someone

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Where is the "edge" of the Universe?
« Reply #10 on: 20/05/2007 21:38:09 »
Ok. if the universe is expanding in all directions, what "space" is it occupying! Is it taking over an area, part of space that was not within our universe? or, as it expands is it creating new "space", or something else?

Since, as I mentioned above, what is beyond our event horizon is unknowable, so we cannot know what space it occupies.

My undersatanding is (and maybe someone will correct me) that the Hubble expansion is actually faster than the expansion of the event horizon, so there is no risk (so long as that situation remains) of new matter entering our universe through the expanding event horizon (on the contrary, if I recollect correctly, we are actually losing matter through that event horizon).
 

Offline Seany

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Where is the "edge" of the Universe?
« Reply #11 on: 20/05/2007 22:58:40 »
Do you think that there is an end to Space?
 

Offline Karen W.

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Where is the "edge" of the Universe?
« Reply #12 on: 20/05/2007 23:44:42 »
There is another topic that deals with this question, but I can't remember what it was called!!
 

another_someone

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Where is the "edge" of the Universe?
« Reply #13 on: 21/05/2007 00:47:44 »
There is another topic that deals with this question, but I can't remember what it was called!!

Not many topics deal with the event horizon, although quite a few deal with the Hubble expansion.

Dealing with the event horizon, we have :
http://www.thenakedscientists.com/forum/index.php?topic=3113.msg24498#msg24498
http://www.thenakedscientists.com/forum/index.php?topic=6676.msg70798#msg70798

(incidentally, in both threads, Ian (SoulSurfer) speculates on the possibility of a universe that does not completely fill our event horizon).

Dealing with Hubble Expansion, we have:
http://www.thenakedscientists.com/forum/index.php?topic=4298.0
http://www.thenakedscientists.com/forum/index.php?topic=6149.0
http://www.thenakedscientists.com/forum/index.php?topic=7675.0
http://www.thenakedscientists.com/forum/index.php?topic=3598.0
http://www.thenakedscientists.com/forum/index.php?topic=2366.0
 

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Where is the "edge" of the Universe?
« Reply #13 on: 21/05/2007 00:47:44 »

 

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